Constant differential temperature controller



Nov. 2, 1943.

I. E. MCCABE CONSTANT DIFFERENTIAL TEMPERATURE CONTROLLER Jmmnunhd oFF DKFI-OST 8 INV ENT OR, /RA E. MfC/QBE ATTORNEY.

Patented Nov. 2, 1943 CONSTANT DIFFERENTIAL TEMPERATURE CONTROLLER Ira E. McCabe, Chicago, Ill. Application June 24, 1942, Serial No. 448,314

(Cl. o-81) 9 Claims.

This invention relates to improvements in devices responsive to changes in temperature for opening and closing electric circuits and more particularly to a device of this character to control the operation of an electrically operated and controlled domestic refrigerator to maintain a predetermined temperature within the cooling compartment thereof.

It is an object of this invention to provide a control device which may be located upon the interior of the box or refrigerator and eliminate the detrimental effect usually encountered in such devices as a result of moisture, corrosion and arcing of an open contact switch by employing a magnetically operated, hermetically sealed mercury tube switch in the control circuit. It is a further object of this invention to provide an actuator for the switch including a temperature responsive element charged with a volatile liquid with means for setting the operating temperature of the switch so constructed that a constant temperature diierential may be maintained for any particular lsetting regardless of the variations of vapor pressures within the charged element resulting from variations in temperature. It is another object of this invention to eliminate bearings in the operating mechanism of this device which might render it inoperative as a result of the effect of moisture and frost upon such-bearings. It is a still further object of this invention to provide manual means to select the temperature to be maintained within the cooling compartment and means cooperating therewith to prevent operation of the switch during periods when it is desired to defrost the cooling coil.

With these and other objects in view, reference is made to the accompanying sheet of drawings which illustrates preferred forms of this invention with the understanding that minor changes may be made therein without departing from the scope thereof.

Figure 1 is a top plane view of a. casing for containing this improved device indicating the operating mechanism in dotted lines and illustrating the temperature responsive element connecting thereto in full lines.

Figure 2' is a view in right elevation of Figure l omitting the temperature responsive element.

Figure 3 is a top plane View of the operating mechanismswitch, and switch adjusting means removed from the casing.

Figure 4 is a fragmentary detail view illustrating the switch and cam supporting and adjusting means in vertical longitudinal section.

Figure 5 is a fragmentary detail view of thel switch operating and adjusting means as shown in Figure 4.

Figure 6 is a similar view of a modified form of switch adjusting means illustrating the switch and switch operating means in dot and clash lines.

The embodiment of this invention as illustrated includes a rectangular casing I for containing the switch operating and adjusting mechanism, said casing provided with a cover 2. A bracket 3 is secured to the front of the casing I to enable the casing to be supported upon the wall of the cooling compartment. An electric circuit connector or plug is passed through an aperture provided therefor in the end wall of the casing and is supported upon the interior by one arm of a U-shaped bracket 5 secured to the front of the casing and. continued in parallel relation adjacent each end wall as shown in dotted lines in Figure 1.

The switch operating mechanism is actuated by an expansible and contractable member preferably in the form of a Bourdon tube 6 mounting at its free closed end and movable therewith a. magnetic switch operator l. The other end of the Bourdon tube `is connected to the interior of a temperature responsive element 8 preferably in the form of a tube and terminating in a coil conveniently located within the cooling chamber and charged with a volatile liquid to increase or decrease the pressure within the Bourdon tube 8 upon changes in temperature of the cooling compartment. The immovable end of the Bourdon tube is mounted upon a supporting block 9 secured centrally upon the bracket 5 at the front of the casing I which block 9 is provided with a port I0 connecting the interior of the Bourdon tube to the interior of the teinperature responsive element 8. A switch support II of resilient metal in the form of a bracket as shown in Figure 3 is supported at one end and secured to the upper surface of the block 9. The opposite free end of the support I I terminates in a portion II e extending parallel to the end of the casing I and is provided with clips for supporting a hermetically sealed, magnetically operated mercury tube switch I2. That portion of the switch support between the clip carrying end IIa and the fixed end, including the bent back portion IIb, is bent at an angle to the bottom of the casing as shown in Figure 3, so that the free end portion II carrying the switch I2 supports the switch with its axis at an angle as shown in Figures 4 and 5.

The hermetically sealed, magnetically operated mercury tube switch I2 is preferably of the type illustrated in the Hunciker Patent No. 2,085,316, June 29, 1937, and is so mounted in the clips on the end II'l of the switch supporting bracket II that the body of mercury will normally be contained in the lower end of the tube in engagement with one electrode of the switch and the other electrode is normally out of engagement with the mercury with the amature on the removable electrode arranged adjacent the bottom side wall of the switch. The electrodes connected by lead wires I2l and I2h to the plug 4. The switch operator 1 mounted on the closed free end of the Bourdon tube 6 is preferably in the form of a plate, as shown in dotted lines in Figure 1, and mounts an electromagnet 1 upon a right angular extension from the plate 1 in such a manner that as the Bourdon tube expands, the electromagnet will be moved in the direction of the pool of mercury in the switch I2 to attract the armature of the switch and close the circuit therethrough and as the Bourdon tube contracts, move the magnet away from the wall of the switch tube releasing the armature from its magnetic field to allow the switch to open.

As the closing of the circuit through the switch I2 in an electrically operated and controlled refrigerating apparatus employed in domestic refrigerators starts the delivery of refrigerant to reduce the temperature within the cooling cabinet, it is desirable to providemeans for opening the circuit when the desired low degree of temperature is'reached within the cooling cabinet. As the temperature within the cooling cabinet descends, the volatile liquid within the temperature responsive element 8 will decrease the pressure within the Bourdon tube '6 allowing it to contract which willv move the magnet 'Ia away from the switch tube I 2 to open the circuit therethrough and cease the delivery of refrigerant. Therefore, it is desirable to provide an adjustment in the mechanism whereby the temperatures within the cooling cabinet which will cause the closing of the switch I2 may be predetermined. To this end, the portion of the switch support II is provided with a downwardly depending cam follower I3 adapted to be engaged and ride over the upper surface of a cam disc I4 mounted between nuts I4a and I4b upon the upper end of a cam adjusting rod I5 passing centrally through the block 9 and provided at its exterior end with a manual operating knob I6. The cam I4 is so constructed that at its lowermost point it will be engaged by the cam follower I3 of the resilient switch support II by engagement of the underside of the nut I4b with the upper end of a sleeve I1 threaded into a bushing I8 passing centrally through and secured to the block 9, the bushing I8 being diametrically slotted for a portion of its length at one end and the halves compressed about the threads of the sleeve I1 to maintain the adjustment. As the cam adjusting rod I5 is rotated by the knob I6, the inclined surface of the cam through follower vI3 will flex that portion of the resilient support I I to cause the switch I2 to be moved away from the front of the casing I until the highest point of the cam is reached. It is preferable to calibrate the relationiof the switch and the magnetic operator therefor so that when the lowest point of the cam engages the cam follower I3 of the switch operating bracket, the lowest temperature desired in the cooling chamber to open the switch may be created. By vproper adjustment of the threaded sleeve I1 with the bushing I8 by the engagement of a tool in the slot I1* provided therefor in the exterior end of the sleeve and with the cam I4 properly positioned by the clamp nuts I4n and I4b upon the adjusting rod I5 the cam can be raised or lowered to contact the follower I3 to position the switch I2 so as to be operated by the magnet. Thereafter manipulation of the knob to rotate the rod I5 and thus the cam will alter the relationship of the switch armature and magnet to raise or lower the degree of temperature necessary to operate the switch. The cam is so designed that when properly calibrated to the temperature prevailing at the element 8 and rotated to its highest point a temperature suiiciently high for defrosting will be established. It is also preferable to provide means for limiting the expansion of the Bourdon tube to a point below the defrosting degree of temperature and to this end, the base of switch supporting bracket II secured to the block 9 is provided with a struck-up projection I9 to be engaged by a stop 20 depending from the plate 'I of the switch operator to prevent expansion of the Bourdon tube upon a rise in temperature moving the magnet into operative position with the switch when the switch has been actuated to the defrosting position.

When the device is calibrated as above described, the switch will be caused to open upon a constant temperature diierentialat any setting irrespectively of Varying vapor pressure conditions created by the volatile liquid throughout the operating range of the controller. In other words, with the temperature element having a liquid charge producing a vapor pressure rise of 5.9 pounds per square inch upon an increase in temperature from 2 to 14 F. and a pressure increase of 10.4 pounds per square inch upon an increase in temperature from 38 to 50 F., this invention by the form of adjusting means provided compensates for the variation in vapor pressures upon a 12 F. change in temperature through the controller operating range by varying the amount of power required to operate the switch. Thus, with each change in temperature setting made by the adjusting knob, an increase or decrease in power necessary to operate the magnetic switch is made to utilize the range of vapor pressures developed by the volatile liquid charged element through a 12 F. change in temperature at the element for the selected temperature setting.

To accomplish the above results, a variation in the operating relation of the switch armature and magnet is made by adjusting the switch in such a manner for different temperatures that at low temperature setting the magnet is operative upon the lowermost section of the armature thus requiring less power and therefore less movement of the magnet to operate the switch. At high temperature'settings the magnet is rendered operative upon the higher sections of the armature closer to the armature spring center where more power and thus a greater movement of the magnet required to operate the switch.

As shown in Figures 4 and 5, the bracket II is so formed that the magnetic switch supported thereby will be positioned in a plane obllquely which the magnetic operator moves. Therefore, not only a more or less movement o! the magnetic operator by the power element is needed (higher or lower operating temperature), but at the same time the power of magneticattraction of .the magnetic operator upon the switch armature is varied thus creating a varying switch operating differential and consequently varying amounts of power to operate the switch. In this manner, the various vapor pressures created by a temperature change of 12 F. at different settings are each made necessary or utilized to affect operation of the magnetic switch for each setting whereby the operation of the switch will take place upon a 12 F. change in temperature at any degree of operating temperature selected throughout the operating range of the controller.

While this invention is particularly applicable to temperature controllers, it is apparent that it mayserve equally as well as a pressure responsive controller wherein the simplicity of structure and elimination of bearings in the active operative parts is desired. Figure 6 of the drawing illustrates the switch supporting portion Ila of bracket Il so formed that movement of the bracket by the cam I4 imparts a direct line movement to the switch I2. Thus in this arrangement no compensation between the magnet and switch is required because operation is desired to be directly responsive to the pressure changes. Changing the position of the switch for operation at diierent pressures moves the switch in a plane which does not alter its relation to the plane through which the magnet operates so that only more or less movement of the magnet is needed to operate the switch. The magnetic effect of the magnet upon the switch for operation of the switch remains the same at eachadjusted setting of the switch.

What I claim is:

1. A constant differential temperature controller for controlling the operation of an electrically operated and controlled refrigerating apparatus lincluding a switch mechanism in the control circuit, means` for operating the switch, temperature responsive means for actuating the switch operating means including a volatile liquid, means for predetermining the temperatureat which the switch operating means will be actuated, including means to maintain a constant operating differential automatically actuated with each temperature setting to alter the relation of the operating means and the switch mechanism to compensate for variations in vapor pressure of said volatile liquid produced by changes in temperature wherein the switch mechanism is a hermetically sealed, magnetically operated mercury tube switch, wherein the operating means for the switch includes a magnet, and wherein the switch actuating means includes an expansible and contractible power element mounting the magnet therecm.

2. The structure of claim 1 wherein said means to maintain a constant operating differential includes a manually operable cam disc and wherein the switch mechanism is mounted upon resilient support and upon rotation the cam disc Ilexes the support to determine the temperature setting at which the instrument operates, and wherein the flexing of the support imparts a movement to the switch tube at an angle to the normal travel of the magnet to compensate for variations in vapor pressure within the power element.

4. A temperature control for an electrically operated and controlled refrigerating apparatus including a magnetically operated mercury tube switch in the control circuit, said switch having a movable armature responsive to a magnetic force to operate the switch, a magnet for operating the switch, a temperature responsive device for actuating the magnet to operate the switch including a Bourdon tube, all containedwithin a casing adapted to be mounted within the cooling compartment of the refrigerating apparatus, a tube containing a volatile liquid located within the cooling compartment and connected to the Bourdon tube within the casing, a resilient support for the mercury tube switch, a manually rotatable cam disc, means upon the resilient support to ride over the cam disc for flexing the support to vary the relation of the'switch armature and magnet to increase or decrease the power required to operate the switch in accordance with the variation in movement imparted to the Bourdon tube for a predetermined change in temperature throughout the range of temperature to which the control is responsive.

5. The structure of claim 4 wherein the ilexing of the switch support imparts a movement to the mercury tube at an angle to the normal path of movement of the magnet to compensate for variations in vapor pressure within the Bourdon tube in accordance with variations in degrees of temperature.

6. The structure of claim 4 wherein the ilexing of the switch support imparts a movement to the mercury tube at an angle to the normal path of movement of the magnet tov compensate for variations in vapor pressure within the Bourdon tube in accordance with variations in degrees of temperature, and wherein a stop is provided for limiting the expansion of. the Bourdon tube at a degree of temperature below the highest degree of temperature to which the switch is responsive.

7. A constant differential temperature control- 1er` for controlling the opera-tion of an electrically operated and controlled refrigerating apparatus .including a magnetically responsive switch in the control circuit, a magnetic actuator for said switch, a volatile liquid charged temperature responsive element for operating said actuator, temperature adjusting means for determining the temperature at which the switch is actuated including means for varying the relation of the switch and actuator to the extent that operation of said actuator by the said temperature responsive element to open and close the switch is dependent upon the vapor pressures developed by said volatile liquid at each respective setting of a resilient support and upon rotation the cam disc flexes the support to predetermine the temperature setting at which the instrument operates.

3. The structure of claim 1 wherein said means to maintain a constant operating differential includes a manually operable cam disc and wherein the switch mechanism is a magnetically operated mercury tube switch mounted upon a the adjusting means through a constant degree of temperature change occurring at each setting wherein the temperature adjusting means includes a cam disc and the last named means comprises an inclined resilient support mounting the magnetically responsive switch and provided with a cam follower adapted to contact the surface of said cam and impart movement to the switch at an angle to the travel of the magnetic actuator upon rotation of said cam.

8. A constant differential temperature controller for controlling the operation of an electrically operated and controlled refrigerating apparatus including a magnetically responsive switch in the control circuit, a magnetic actuator for said switch, a volatile liquid charged temperature responsive element for operating said actuator, temperature adjusting means for determining -the temperature at which the switch is actuated including means for varying the relation of the switch and actuator to the extent that operation of said actuator by the said temperature responsive element to open and close the switch is dependent upon the vapor pressures developed by said volatile liquid at each respective setting of the adjusting means through a constant degree of temperature change occurring at each setting, wherein means are provided to limit movement of the magnetic actuator by the temperature responsive element at a degree of temperature below the highest degree of temperature operation determinable by the temperature adjusting means.

9. A constant differential temperature controller for controlling the operation of an electrically operated and controlled refrigerating apparatus including a magnetically responsive switch in the control circuit, a magnetic actuator for said switch, a volatile liquid charged temperature responsive element for operating said actuator, temperature adjusting means for determining the temperature at which the switch is actuated including means for varying the relation of the switch and actuator to the extent that operation of said actuator by the said temperature responsive element to open and close the switch is dependent upon the vapor pressures developed by said volatile liquid at each respective setting of the adjusting means through a constant degree of temperature change occurring at each setting, wherein the temperature adjusting means includes a cam disc and the last named means comprises an inclined resilient support mounting the magnetically responsive switch and provided with a cam follower adapted to contact the surface of said cam and impart movement to the switch at an angle to the travel of the magnetic actuator and means limiting movement of the magnetic actuator by the temperature responsive element at a degree of temperature below the highest degree of temperature operation determinable by the temperature adjusting means.

IRA E. MCCABE. 

